bpo-33641: Convert RFC references into links. (GH-7103)


85% of them are already links.
(cherry picked from commit 0a36ac1a09587735237c5978ebd046313922869c)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
diff --git a/Doc/library/nntplib.rst b/Doc/library/nntplib.rst
index 2c3cd8d..d8ef8a6 100644
--- a/Doc/library/nntplib.rst
+++ b/Doc/library/nntplib.rst
@@ -542,7 +542,7 @@
       is supplied, then the returned *list* is an empty list. This is an optional NNTP
       extension, and may not be supported by all servers.
 
-      RFC2980 says "It is suggested that this extension be deprecated".  Use
+      :rfc:`2980` says "It is suggested that this extension be deprecated".  Use
       :meth:`descriptions` or :meth:`description` instead.